Often for unknown reasons, >10% of patients undergoing surgery for lumbar back pain experience ‘failed back surgery syndrome’ (FBSS). The recent discovery of pathobiont gut bacteria in degenerative intervertebral discs prompted a ‘gut-disc axis’ hypothesis. Should the microbiome-mediated inflammation and disc colonisation persist postoperatively, the surgery's success may be undermined. This pilot aims to determine whether the microbiome may therefore aid to explain FBSS. Following IRB approval, 8 participants completed the Visual Analogue pain Scale (VAS), Oswestry Disability Index (ODI), and EQ-5D, preoperatively and at 12 weeks and 6 months post-operatively. A faecal sample was collected pre-operatively and microbial DNA was extracted for species-level 16S rRNA amplicon sequencing. Associations between taxa abundance, alpha-diversity, percentage score change, and achievement of the minimum clinically important difference (MCID) were statistically investigated. There was notable phylogenetic clustering of successful and unsuccessful surgical outcomes. Shannon index was positively correlated with percentage improvement in ODI at 6 months’ follow-up (p<0.05), but not with achievement of the VAS or ODI MCIDs. Mean abundance of the Proteobacteria phylum and Prevotella copri species was significantly higher among participants who failed to achieve the MCID for both VAS and ODI at 6 months’ follow-up (p<0.05). This is the first study to implicate a Prevotella-dominant enterotype, elevated Proteobacteria abundance and low-diversity dysbiosis in a heightened risk of FBSS. Studies of higher power are required to estimate the effect sizes of these associations, investigate causation, and consider the viability of synbiotic therapy to improve spine surgery outcomes.